This invention relates to an improvement in friction disc packs for wet disc brakes wherein the co-efficients of friction of the friction plates varies across the pack.
Wet disc brakes are utilized in many vehicle braking applications. They are also used in many non-vehicle braking applications. In particular, a number of rotating discs are provided with a friction surface, and are connected for rotation with a wheel hub. The discs are slidable axially along the wheel hub. The rotating discs are interspaced with stationary discs which are connected to an outer stationary member. The stationary discs are also axially slidable relative to the outer stationary member.
A hydraulic chamber is associated with a piston, and when hydraulic fluid is delivered to the chamber, the piston moves to compress the rotating and stationary discs together to reduce the rotation of the rotating member relative to the stationary member.
These types of brakes typically include a plurality of interspaced stationary and rotating discs. Often, as many as ten rotating discs are used in combination with eleven stationary discs.
The discs are spaced at one end of the piston, and a reaction surface of the stationary housing is at the opposed end of the discs. Thus, the piston pushes the discs together and against the opposed reaction surface. A rebound force is created from the opposed reaction surface back into the discs. The piston force is applied directly on the discs closest to the piston.
Applicant has found that there is not a constant force across the discs. Rather, the discs closest to the piston, and the discs closest to the opposed wall, see the greatest force. Applicant has also found that due to this, the discs adjacent the two ends of the disc pack experience the most wear, and need to be replaced more quickly than more centrally located discs. However, the friction discs and stationary discs are replaced as a pack, and thus the centrally located discs may not be worn when replaced.
Due to this phenomena, disc packs do not have as long a life as they would otherwise have. If there were more uniform wear, then the life of the disc pack could be increased.